This project consists of two related parts,which, taken together, form the cornerstone for the achievement of a longer range goal. In the first part of the project, the plan to develop a quantitative description of the heart as a pump under in vivo conditions and taking itno account its time-varying properties will be continued. In the second part, a range of data obtained from animal experiments will be interpreted for the purpose of arriving at a deeper understanding of the physical phenomena observed in arteries. These two parts will extend the basis for a further analysis of the interaction between the ventricle and the arteries, the long range goal of this project. The newly discovered similarity principle will provide a solid foundation to pursue this work.